In recent years, communication systems and services have continued to advance rapidly in light of various technological advances and improvements with respect to telecommunication networks and protocols, in particular packet-switched networks such as the Internet. A considerable interest has been focused on Voice-over-Packet systems. Generally, Voice-over-Packet (VoP) systems, also known as Voice-over-Internet-Protocol (VoIP) systems, include several processing components that operate to convert voice signals into a stream of packets that are sent over a packet-switched network such as the Internet and convert the packets received at the destination back to voice signals. One of the processing components in a VoP system is a device called echo canceller that is used to perform echo cancellation. An echo canceller can be implemented as one of the components included in a digital signal processing (DSP) chip or device (also called digital signal processor herein). A DSP device may include one or more digital signal processor cores that perform the processing of voice and/or data signals and a global memory that is used by various components of the DSP device to perform their corresponding functions. For example, an echo canceller in a DSP device may require a large amount of dynamic memory in the global memory to perform its echo cancellation function.
Generally, the dynamic memory required by the echo canceller to perform its corresponding function is transferred via direct memory access (DMA) mechanisms into and out of the DSP cores from and to the global memory for every frame. A frame can be defined as a time interval over which processing functions are performed to generate a corresponding voice packet from corresponding voice input signals. Typically, a DSP device can be configured to perform voice and packet processing for multiple VoP channels and each VoP channel can have its own persistent dynamic memory storage in the global memory. Accordingly, the number of VoP channels that can be processed by a DSP device depends, among other factors, on the dynamic memory requirements of the echo canceller functional block. Thus, higher channel densities can be achieved if the dynamic memory requirements of the echo canceller can be reduced without significant quality impairment of voice signals.
In general, a substantial portion of the dynamic memory requirements of an echo canceller is allocated for storing filter coefficients (also called coefficients herein) that are used in the echo cancellation process. One way to reduce the storage requirements for coefficients is to compress them using lossless compression methods such as Huffman coding, arithmetic coding, etc. While lossless compression methods can be used to ensure that there are no quality impairments to the voice signals in performing echo cancellation, lossless compression methods have various disadvantages as follows:                Lossless compression results in variable number of memory (e.g., bits) requirement per frame. Therefore, channel densities can be increased on a statistical average basis, but not deterministically.        In the worst case, the number of bits required to store the coefficients can be higher than that by not doing any compression. This case can be avoided by using lossless compression (lossless coding) only when it helps. However, information regarding whether or not lossless coding is done needs to be stored as side-information with a small increase in storage requirement.        The entropy of echo-canceller coefficients (the theoretical lower limit on bits per coefficient requirement) using one-dimensional symbols turns out to be 10 and a few tenths of a bit. Thus the best-case savings in memory using one-dimensional lossless coding is not even 50%.        The complexity of lossless coding and decoding is high.        
In contrast, lossy compression methods can overcome the disadvantages of lossless compression methods, but could result in quality impairment. Accordingly, there exists a need to reduce the memory requirements of echo-cancellers without significant quality impairment to the voice signals.